In response to a recent trend toward higher performance of an engine, many combustion pressure sensors for detection of combustion pressure in a combustion chamber have been suggested with the intention of controlling a combustion state in the combustion chamber precisely.
There has been a suggested pressure-measuring glow plug used for a diesel engine in which a conventional combustion pressure sensor is provided. The pressure-measuring glow plug includes a cylindrical plug body that can be fitted in a cylinder of a diesel engine, a heating rod housing a heat generator that generates heat in response to conduction of a current, the combustion pressure sensor that outputs an electric signal in response to the load of the heating rod moving under pressure in the cylinder, and others. The heating rod is rigidly connected mechanically to the combustion pressure sensor and a bellows. The bellows is arranged as a sealing element between the heating rod and the plug body. The bellows elastically supports the heating rod 51 in the axial direction in the plug body to allow the heating rod 51 to allow friction-free movement thereof (see patent literature 1, for example).
There has been a suggested combustion pressure sensor according to a different background art functioning as a high-temperature pressure sensor. In this sensor, if the pressure of a high-temperature fluid acts on a measurement target pressure reaction surface of a diaphragm, the diaphragm deflects. This deflection is transmitted through a pressure transmitting member to a strain sensitive element. The strain sensitive element outputs an electric signal responsive to received pressure. A central part of the diaphragm is depressed to a side opposite the high-temperature fluid. This achieves favorable measurement accuracy without causing an output error due to heat (see patent literature 2, for example).
There has been a suggested combustion pressure sensor according to a different background art provided in a spark plug. The spark plug has an insulator formed around a center electrode, and a washer member electrically connected to a lateral electrode and formed around the insulator. The combustion pressure sensor includes a piezoelectric element made of lithium niobate and arranged between the insulator and the washer member and near a spark gap between the center electrode and the lateral electrode (see patent literature 3, for example).